Thursday, February 2, 2012

An Unseasonably Warm Pruning Winter

Contributing writer - Jabbari Brew, Tree Planting Crew

Pruned branches at Casey Trees headquarters.

The first month of the new year is behind us. The field crew's work in January focused on American elms - both planting and pruning. So far we have pruned trees all over the District, along corridors like Massachusetts Avenue, Piney Branch Parkway, East Capitol Street and Nebraska Avenue. We have touched 300 trees in some way, whether it was removing dead or broken branches, structurally pruning, or raising the crown. Pruning trees in the winter is the best practice, as the trees are dormant and the risk of pest problems associated with pruning cuts are minimized, plus the tree has all of the growing season ahead to compartmentalize the wounds. Also the tree is naked in the winter, so it is a lot easier to see the structure of the tree.

At the beginning of January, I fretted about pruning in the cold winter. The thought of climbing up a six-foot ladder to reach a couple of branches in freezing temperatures gave me the shivers. But to my surprise, it has been a pretty warm pruning season. The average temperature on a working day in January was 49 degrees Fahrenheit, and the last day of the month was 65 degrees. It was so warm it felt like we should have been planting trees - not pruning. The warm weather has made pruning more enjoyable. I spent more time with the tree, finding defects to fix and enhancing the structure of the tree, instead of hustling to get back in the warm truck.

Our pruning work focuses on establishing good tree structure and reducing the risk of failures from, for example, co-dominant stems, which are very common in elm trees. Structural pruning is beneficial for several reasons: it helps the tree establish a strong leader, enhances the tree's appearance and form, and influences the ultimate size of branches.

In the field it is fairly easy to judge what works needs to be done in a tree. We like to say, "hit 'em up, hit 'em hard," when the trees are young. Structural pruning is easier on younger, established trees because it is easier to reach the limbs from a ladder and make the cuts. More importantly, the size of the wounds from the cuts will be smaller, and the tree will be able to seal those wounds quicker. For trees that aren't established (trees that have been in the ground for less than two years), we only inspect for damaged or broken branches. On older trees our work is limited to how high we can safely reach with our tools from the ladder. Also with larger limbs, sometimes greater than five inches in diameter, the work becomes more dangerous to both the crew and the tree.

Jabbari pruning a young American elm last winter.

Warm weather has made this pruning season really enjoyable, but it may cut our work short. There's a saying that "pruning is a double-edged sword" - a double-edged saw, I would rather say. Pruning a tree can help or hurt a tree depending on where, when and how the cuts are made. Over the next few days and week we will be carefully observing whether buds are beginning to swell and break. We don't want to prune during bud break or when the leaves are flushing out. I don't know if six more weeks of winter are in store, but the groundhog, Punxsutawney Phil, saw his shadow today, so maybe I will still get some of that dreadful cold winter weather. Fingers crossed.